1. Field of the Invention
This invention relates to a conductive contact material used for various devices such as an electrizer, deelectrizer, development device, and transfer device of an electrophotographic and electrostatic image forming apparatus, and more particularly relates to a conductive contact material consisting of component molecules which does not decompose and does not soil an image carrier, etc. not only in initial use but also in repeated use to maintain the quality of the formed image at high level.
2. Description of Related Art
In electrophotographic and electrostatic image forming apparatuses used for copying machines, FAX machines, and printing machines, a charger is used for an electrizer, deelectrizer, transfer device, etc. Heretofore, devices which utilize corona discharge phenomenon such as a corotoron charger have been used predominately as the charger. However, recently contact type chargers are used widely to reduce ozone generation. Because a contact type charger has a conductive contact material which is in contact with a charged body such as an image carrier, component of the contact material partially can adhere to the charged body and cause chemical change to soil the charged body. Particularly, when direct contact continues for a long time, for example, during resting, a charged body is apt to be soiled.
Such soil causes following problems. In the case that a charged body is an image carrier consisting of photosensitive material or dielectric material, photosensitivity or electrification property of a soiled portion deviates from a normal value to cause image noise. In addition, friction coefficient of a cleaner material deviates from the normal value at a soiled portion to cause irregular motion, and the irregular motion causes also image noise. In the case that the charged body is a transfer conveyer belt or intermediate transfer body, deviation of resistance value, electrification property, and friction coefficient of a soiled portion from a normal value causes image noise.
In particular, when an image forming apparatus is used repeatedly for a long time, soiling due to component of the conductive contact material becomes remarkable. The soiling is attributed to ozone and NO.sub.x which attack the conductive contact material around the portion where oxygen and NO.sub.x are generated. Since a little ozone and NO.sub.x are generated because of charging by applying discharge even though a contact charging device is used. Molecular chains of resin material which is a base material of the conductive contact material are fragmented to generate active monomers and origomers, which can be a soiling source. In particular, use of an organic ion conducting agent having a large molecular weight added to provide electric conductivity facilitates scission of molecular chain of the ion conducting agent due to ozone and NO.sub.x to generate origomers, and results in increased soiling of the charged body. Further, an organic ion type conducting agent is not preferable because it functions as a plasticizer itself due to its large molecular weight to cause bleeding, from this view point of soiling source an organic ion type conducting agent is not preferable.
Various measures has been taken to avoid soiling. For example, Japanese Unexamined Patent Publication No. Hei 5-333724 discloses an image forming apparatus in which a transfer roller is rotated with linking to a photosensitive drum namely charged body, and when the photosensitive drum is brought to a stop the transfer roller is separated from the photosensitive drum. In the image forming apparatus of this patent, conductive contact material of the transfer roller is prevented from being in contact with the photosensitive drum for a long time in order to suppress soiling of the photosensitive drum due to component of the conductive contact material. Japanese Unexamined Patent Publication No. Sho 58-87572 discloses an image forming apparatus provided with a transfer roller having the surface which is coated with epichlorohydrin rubber. The image forming apparatus helps prevent a charged body from being soiled due to conductivity of a transfer roller and component of a contact member.
However, the conventional image forming apparatuses disclosed in the above-mentioned publications can not solve the problem described herein under because a conventional conductive contact material is used as it is. In detail, an image forming apparatus disclosed in Japanese Unexamined Patent Publication No. Hei 5-333724 is inevitably large sized and requires increased number of parts because the apparatus requires a mechanism for rendering a transfer roller movable from a photosensitive drum. On the other hand, an image forming apparatus disclosed in Japanese Unexamined Patent Publication No. Sho 58-87572 complex manufacturing process for forming a coating layer on a transfer roller results in increasing the percentage of defective product.
The present invention is accomplished to solve the above-mentioned problems of the conventional arts. In detail, the object of the present invention is to provide a conductive contact material which does not soil a charged body due to component thereof not only during initial use but also after repeated use, and to reduce disadvantages such as image noise due to soil on a charged body without involving a large image forming apparatus and complex manufacturing process.
To solve the above-mentioned problem, the conductive contact material of the present invention consists of base material of thermoset urethane containing an antioxidant and an inorganic ion electrically conducting agent. The antioxidant is preferably of a radical chain terminator type. The antioxidant content is preferably in a range from 0.1 to 3.0% by weight. The electrically conducting agent content is preferably in a range from 0.01 to 2.00% by weight.
The conductive contact material contains an inorganic ion electrically conducting agent in order to render the electrically conductive contact material electrically conductive. As the result, the conductive contact material is corrosion-resistant to ozone and NO.sub.x different from a conductive contact material containing an organic ion electrically conducting agent, therefore can not be a remote cause of monomers and origomers which are cause of soiling. An inorganic ion electrically conducting agent remains homogeneously in the base material differently from an electrically conducting agent of electron conducting type such as carbon and metal oxide, therefore electrical conductivity is even through the base material. Further, an antioxidant contained in the conductive contact material in an suitable amount prevents molecular chains of thermoset urethane namely the base material from being attacked by ozone and NO.sub.x, and as the result, generation of monomers and origomers due to scission of molecular chains is prevented. In particular, because of radical type oxidation mechanism of ozone and NO.sub.x, the radical chain terminator type antioxidant is very effective. Examples of radical chain terminator type antioxidant include hindered phenols and aromatic amines.